At a survey site, it is common to measure azimuth angles, elevation angles, and distances of a plurality of survey points with respect to a single reference point. In such a case, conventionally, two workers have been necessary, namely, one worker for moving a reflecting prism between the survey points and another worker who is at the reference point, for collimating the reflecting prism located on each of the survey points by looking through a collimating telescope of a surveying instrument located on the reference point.
In recent years, surveying instruments including automatic collimators or automatic trackers have been put into practical use. An automatic collimator is a device for automatically collimating a reflecting prism by rotating a collimating telescope, while an automatic tracker is a device structured to rotate a collimating telescope automatically so as to always maintain a reflecting prism in a collimated state. When a remotely controllable surveying instrument including an automatic collimator or an automatic tracker is used, the surveying instrument can be controlled by a remote control from the reflecting prism side, and thus the worker on the reference point side becomes no longer necessary.
However, in a surveying instrument including an automatic collimator, there has been a problem that it takes time for the surveying instrument to find a reflecting prism if the collimating telescope is not pre-directed in the direction of a reflecting prism. If with a surveying instrument including an automatic tracker, measurement can be immediately performed after placing a reflecting prism at a survey point, but when moving the reflecting prism, it has been necessary to move the reflecting prism slowly so as not to stray away from the field of view of the collimating telescope while always directing the reflecting prism toward the surveying instrument. There has been a problem that, if the reflecting prism strays away from the field of view of the collimating telescope as a result of directing the reflecting prism in a direction different from that of the surveying instrument, quickly moving the reflecting prism, or an obstacle being located between the surveying instrument and reflecting prism, automatic tracking can no longer be performed.
In order to solve such problems, a total station (combination electronic transit and electronic distance measuring device) has been proposed (refer to the following patent document 1), for which each of the total station and reflecting prism includes a GPS receiver, and receives radio waves from GPS satellites to determine the position of each of the total station and reflecting prism and calculate the azimuth angle and elevation angle of the reflecting prism when viewed from the total station, so that the collimating telescope can be immediately directed toward the reflecting prism at the time of measurement by using the azimuth angle and elevation angle.